A. Field of the Invention
The present invention generally relates to integrated circuits. In particular, it relates to forming a diffusion barrier layer comprising a self-assembled monolayer in an integrated circuit.
B. Description of Related Art
Copper is becoming the metal of choice for forming conductive patterns in integrated circuits. There are, however, unresolved issues with its use. For instance, copper diffuses rapidly in silicon and silicon dioxide. The diffusion, over time, results in junction linkage, which decreases device efficiency.
To address the problem of copper diffusion, researchers have developed “diffusion barriers.” A diffusion barrier is part of the metallization scheme, comprising a layer of material formed between an overlying copper layer and an underlying silicon or silicon dioxide layer. The diffusion barrier serves to inhibit the diffusion of copper into the surrounding layer.
The use of amorphous alloys as diffusion layers has been discussed. Amorphous binary silicides, such as molybdenum-, tantalum and tungsten silicide and amorphous ternary alloys (e.g., Ti—Si—N) have been reported as diffusion barriers. The formation of these layers uses sophisticated processes, such as sputtering and/or chemical vapor deposition, or their variants. This results in the inclusion of substantial contaminants and residual stresses. Perhaps more importantly, these films have poor continuity and uniformity in non-planar structures.
Diffusion barriers made of TiN, TiSiN and TiN/TiSiN have also been reported. Many of the processes to form these layers involve treatments such as nitridation, oxidation, and post-deposition annealing.
While a number of diffusion barriers have been discussed in the art, improved diffusion barriers are desirable, especially those that are very thin and continuous.